Nucleophilic Reaction of 1,8-diazabicyclo[5.4.0]undec-7-ene and 1,5-diaza-bicyclo[4.3.0]non-5-ene with Methyl Pheophorbide a. Unexpected Products
Ma, L. and David Dolphin
Trialkylsilyl triflates promote the direct nucleophilic reaction of “non-nucleophilic DBU and DBN” with methyl pheophorbide a to give substituted chlorin e6 amides, where the bicyclic bases have undergone ring opening. The reaction most likely results from coordination of trialkylsilyl triflates to the β-ketoester, forming an ion-pair intermediate. The adduct is so strongly electron-deficient that it can electrophilically attack the nonbonding nitrogen electron pairs in DBU and DBN.